The present invention relates to a method and apparatus for extending the range and accuracy of electronic and electro-optical systems for determining the distance from a reference object to another object. A multiplicity of range baselines is employed, and a computer is used to automatically switch between base lines to extend the total measurement range, to increase the precision of range measurement over a prespecified set of ranges, or both.
Electronic systems which accurately measure the distance between a reference point and a distant object are of great value for a variety of purposes and in a broad range of applications, one of the most common being autofocus cameras. To measure range, various systems have been developed which are based on a variety of physical principles and which are successful in varying degrees for various purposes. For use in air, sonar ranging systems exist which emit an ultrasonic beam and measure its round trip time to the object of interest. Given the known speed of sound in air, the round trip time contains the information necessary to allow the calculation of the distance between ultrasound source and the object of interest. Ultrasonic systems have been successfully used in autofocus cameras and in portable aids to measure the distance to an obstacle for visually impaired people. A substantial disadvantage for some applications, and an advantage for others, is that the ultrasonic beam is reflected by some transparent objects and thus cannot measure the distance when, e.g., a glass window is interposed between the sound source and the object of interest.
At least two other types of autofocus/range-measuring systems are used in cameras. One employs passive sensors (typically charge-coupled-devices --CCDs), while the other is based on the principal of triangulation and utilizes a collimated beam of light, usually infrared (IR) light. The IR system is very widely used in autofocus cameras, particularly in relatively low-cost units. Not without its disadvantages, the IR system has received the benefit of considerable development over the last decade, and such systems are now commercially available which are capable of accurately measuring the distance between IR source (for camera or other range-measuring application) and object of interest, even in the presence of competing signals such as fluorescent or incandescent lights or the infrared component of sunlight. A representative high-quality IR system is described in16-STEP RANGE-FINDER IC H2476-01, Hamamatsu Corporation, 360 Foothill Road, Bridgewater, N.J., 08807-0910, incorporated herein by reference. The reference IR system can accurately divide the distance between IR source and object into 16 "focus zones", where each of the focus zones is sufficiently well determined that the zone signal can be used to accurately focus the lens of a camera over all distances from about one meter to infinity. By employing a different optical design optimized for measuring small distances, the same electronic system can be used to accurately measure very small differences in distance, down to small fractions of a millimeter. Proximity gauges based on the IR system are one example of applications for this close-measuring capability. No single, integrated system is available or has been described, however, which can accurately measure small distances representative of those of a proximity gauge ranging up through the distances representative of close-up photography (a few millimeters up to a maximum distance of about 1 meter) and continuing to and including those distances representative of conventional photography (typically 1 meter to infinity).
Many inventions have been described for automatically measuring range. In Stimson, U.S. Pat. No. 3,435,744, an automatic focusing system is disclosed for a camera which utilizes an emitting beam and a receiving photocell. A lens which is mounted on a reciprocating mechanism and aligned with the photocell is moved so as to obtain the maximum intensity of reflected light. A distance measurement is computed according to the lens position at which the reflected light is greatest. Pagel, U.S. Pat. No. 3,442,193, discloses an improvement to Stimson which provides a means to actuate the rangefinder with a camera trigger and open the camera shutter after focus is obtained.
Larks, U.S. Pat. No. 3,511,156, teaches a method for splitting an image and comparing the position of each portion. If the portions coincide, the image is in focus, if not, correction is made.
Frazee, et al., U.S. Pat. No. 3,751,154, uses a pair of photodetectors which are moved side to side to determine object distance. The circuitry compares the signal from the two photodetectors to obtain equal signals from each. The angular position at which the signal from the two detectors is equal is used for a triangulation computation of the focal distance.
Tamura, U.S. Pat. No. 4,44,477, discloses a method of comparing the amplitude of reflected light with a reference amount. The differences may be positive or negative and relate to the distance zone of the object to be photographed.
Takagi, et al., U.S. Pat. No. 4,482,234, teaches an apparatus and method for rapidly focusing a camera wherein the full range of focus distance is divided into several ranges. The camera operator selects one of the ranges with a selector switch. The circuitry of the camera then checks the distance and adjusts the lens within the selected range.
Kawabata, U.S. Pat. No. 4,582,424, discloses a system in which a series of light sources and a series of light detectors are coupled through analytic circuitry to obtain distance measurement. By the combination of source transmissions and detector receptions, the distance by zone is determined.
Matsuda et al., U.S. Pat. No. 4,768,053, teaches an apparatus and method of measuring distance through the use of a number of light sensitive diodes positioned selectively. According to the different quantities of light on each diode, the distance to an object can be calculated by triangulation.
Ishiguro, U.S. Pat. No. 4,814,810, discloses an apparatus incorporating a light source and a plurality of light detectors. The position of reflected light on the light detectors is accurately related to the distance of the object.
None of the cited inventions or other known prior art employ or suggest the employment of the apparatus and method of the subject invention, namely, the use of multiple sets of focus zones designed into hardware and programmed to switch automatically via computer control between focus zone sets to extend the range measurement capability to accurately measure object distances from very small to very large.